Field of the Invention
The present invention relates to a digital torque wrench, more particularly to a digital torque wrench which is handy to preset a torque value and can release precisely when the torque applied to a fastener reaches the preset torque value.
Brief Description of Prior Art
Referring to U.S. Pat. No. 6,119,562, U.S. Pat. No. 6,276,243 and U.S. Pat. No. 6,526,853, the torque wrench in each case substantially comprises a release mechanism provided therein. The release mechanism mainly employs a linkage formed by a number of levers to carry out the release action. If applied torque exceeds preset torque value, when the torque wrench is used to tighten a bolt, the release mechanism will conduct release action so that the torque wrench becomes ineffective in tightening. However, this release mechanism in implementation has the problems of slow response action among the levers, taking much more force and sluggishness in performing release action. Moreover, the release action becomes unreliable due to aging, deformation or elastic fatigue of a restoring spring after using for a period of time. Furthermore, when the preset torque value is about to be reached, the counter moment of the linkage of the release mechanism will drop down sometimes. At this moment, if too much force is applied, the torque value will quickly rise again and go beyond an upper limit value to cause torque value error. This will result in unreliable tightening of fastener.